When printing black-and-white on variable contrast paper with a color-head enlarger, the usual tactic is to make a single exposure through a discrete filter, such as 20M (magenta) or 50Y (yellow). That specific filter is selected to afford good overall contrast to the print, which may then be fine-tuned by dodging or burning selected portions of the image. An alternative technique—so-called split-filter printing—is to expose a print twice, once through an intensely magenta filter and then through a strong yellow filter (or vice-versa). With this approach the relative times for the two exposures are adjusted to create a print of the correct overall contrast. The idea is to use a magenta exposure that provides good shadows to the print and a yellow exposure that will secure good highlights. We have seen writers claiming that this technique produces better results, but PT Editor Scott Lewis was told years ago that this latter technique produced results similar to using a filter in-between the two extremes, with no particular benef it other than more busy work. He asked us to do some comparative testing. Specifically, we were interested in three things:
• Do both approaches afford easy access to the same range of print contrasts (grade numbers)?
• If so, are the curve shapes (the path from shadow to highlight) the same with both techniques when adjusted to produce the same grade number?
• And, if so, how do exposure times compare?
We explored these issues, once again using one of the darkrooms of Edgar Praus (4photolab.com). Edgar operates a full service traditional-digital custom lab that may well be the last one remaining between Toronto and New York City.
Figure 1 examines the contrast range available when the color head is used in its traditional mode with glossy Ilford Multigrade IV RC Deluxe Paper. We made several step-tablet exposures with single filters ranging from 180Y to 180M, and measured the resulting contrasts for each, expressed here as grade numbers. The relationship is not particularly smooth, but it is clear that filtration can be identif ied that will yield any grade number from about a minus one to nearly five.